Was the idea here that Yutaka and Minami are more akin to the manga stereotype and Konata and Kagami are more like reality?

Or was the whole thing just a pretext to Kagami's infuriated and embarrassed expression?

I'd say both of it. lol

The terms used are 'yuri' and 'bian'; the latter is how Japanese lesbians refer to themselves. It derives from 'rezubian', which is a somewhat negatively connoted term and also known by the public. 'Bian' is an insider term.